This invention relates to electrooptical devices, and more particularly to devices wherein the electromagnetic radiation transmission characteristics may be reversibly altered by a suitably controlled electric field.
The present invention provides an electrochromic device wherein the change of color only occurs above a certain applied threshold voltage. The electrochromic cell is analogous to a battery in that it is an electrolytic device which generates an internal electromotive force which is uniquely determined by the color state of the device. That is, the EMF that can be measured across the cell at any given time is dependent upon the color state and degree of coloration of the device. For a particular device, it is possible to make the EMF in the colored state sufficiently different from the EMF in the uncolored state so as to allow electronic sensing of the color and hence digital programing of the device. This novel device has the additional characteristic that its response to an applied field is nonlinear in nature. The aforementioned characteristics of the device makes the device suitable not only as an electrochromic display device but also as both a light addressable and electrically adressable memory element.
The prior art devices such as the one described by S. K. Deb et al. in U.S. Pat. No. 3,521,941 differs from the novel device in that it is not an electrolytic device and does not generate an EMF which is uniquely determined by the color state. It further differs in structure from the novel device in that the novel device does not contain a current carrier permeable insulator as described in Deb et al.
While the structure of the novel device is similar to that described by Meyers in U.S. Pat. No. 3,708,220, the examples of the device as set forth in Meyers do not exhibit a unique threshold which is determined by the color state of the device nor is the device as particularly described in Meyers a nonlinear device.